Radio frequency transmitter



Flpalo? OR 391149107 SEARCH [mm/ De- 10, 1963 J. l.. wHlsENHuNT3,114,107

R RADIO FREQUENCY TRANSMITTER SUBSTWUTE PQR MlSSNG o Filed Dec. e, 196025 ,ef/lne.

United States Patent O M 3,ii4,i7 RADI@ FREQUENCY TRANSMETTER (E. L.Whisenhunt, Reseda, Calif., assigner to Packard- Bell ElectronicsCorporation, Los Angeles, Calif., a corporation of California Filed Dec.6, 1969, Ser. No. '745133 3 (Ilaims. (Cl. S25-195) This inventionrelates to transmitters and, more particularly, to transmitters for usein inexpensive remote con-trol systems.

Competitive remote control system-s utilize high frequency carriersmodulated by bursts of audio frequency tones or signals. Such systemshave application, for example, to remote controlled equipment such asmodel airplanes, trains, boats, garage doors, etc. In such cometitivesystems, the cost of the various components is,

of course, an important aspect of the commercial Success of the systems.In prior transmitters for such systems, a number of stages have beenrequired including a radio frequency oscillator, an audio frequencyoscillator, ampliiiers and a modulator'for modulating the audiofrequency signal on the radio frequency carrier. These equipmentrequirements cause the transmitters to be relatively expensive.

In a specific illustrative embodiment of this invention, a separatemodulator is not required and, moreover, a separate modulatingtransformer is not required. The elimination of such componentsmaterially reduces the cost of the remote control system which includesthe transmitter. lie transmitter includes an audio oscillator stagehaving an auto-transformer which forms part of the feedback path for theoscillator and which also senves to provide the audio frequency signalfrom the oscillator to a radio frequency output coil. The audiooscillator is also a power oscillator as the auto-transformer resonatesat the audio frequency to provide for 100 percent modulation of theradio frequency signal at the output coil. The radio frequency signal isdeveloped by a crystal oscillator coupled to the radio frequency outputcoil.

Features of this invention relate to introducing the audio frequencysignal in series with the radio frequency output coil to provide for thel() percent modulation of the radio frequency carrier. The audiofrequency signal is provided through a DC. meter which serves todecouple the radio frequency signal from lator and to tune the crystaloscillator and the output coil for maximum signals.

Further features of this invention relate to means for readily changingthe amplitude of the audio signal without varying its frequency and forgiving the uniform audio amplitude with variations of componentcharacteristics. The radio frequency output coil is inductively coupledto the antenna of the ransrnitter. v

Further advantages and )features of this invention will ecome apparentupon consideration of the following description when read in conjunctionwith the drawing wherein:

The single FIGURE is a circuit representation of the transmitter of thisinvention.

Referring to the single figure, a single source of potential 14, whichmay be a battery providing a potential of 9 volts, is utilized toenergize the various components of the transmitter shown in the ligure.The 9 volt pothe audio oscil- :ill/nid? Patented Dec iti, i963 tentialis provided from the source M through a switch l5 to energize a radiofrequency oscillator iti, a radio frequency amplifier il, and an audiofrequency oscillator l?. which together form the transmitter of thisinvention.

The oscillator lib is a crystal controlled oscillator having a crystal17 in the feedback path between-the collector and emitter electrodes ofa junction transistor 2l). The grown diffused transistor Ztl mayillustratively be of the type R425 manufactured by the Texas InstrumentCompany. The crystal I7 may be tuned, illustratively, to a frequency of27 rnegacycles so that Ithe oscillator 1li provides a 27 megacyclesignal.

rf'he transistor Ztl is biased by a connection from the switch i5through a base resistor 21 :and the emitter is biased from groundthrough an emitter resistor 22. The resistor 2l may, illustratively,have a value of 27 kilohms and the resistor 22. may, illustratively,have a val-ue of 27() ohms. The base electrode of the transistor 2d isalso coupled to ground by a resistor 23 having a suitable value such as4.7 kilo'hms and by a capacitor 24. having a suitable value such as0.002 microfarad The source 14 forward biases the transistor Ztl causingit to become conductive and to couple a positive potential from itscollector electrode through the primary winding of a transformer 25 tothe crystal 17 which is coupled between a tap of the primary winding ofthe transformer 25 and the emitter electrode of the transformer 2li. Theprimary winding of the Itransformer Z5 is shunted by an adjustablecapacitor 27 which is utilized to t-une the transformer 25 so as tocouple a maximum signal to a radio frequency amplier Ill.. The capacitor27 may have a suitable range such as l to 2() micromicrofarads. Thelower junction of the capacitor 27 and the primary winding of thetransformer 25 are connected by the switch l5 to the source le.

The crystal oscillator it? develops the 27 megacycle carrier signal andcouples it to the emitter electrode of a junction transistor 3@ in theradio frequency amplifier 1l. The transistor 39 may be of the same typeas the transistor 20. The base electrode of the transistor 3@ isconnected to ground and its collector electrode is connected to thejunction of la radio frequency output coil 32.. The coil 32 is shuntedby an adjustable capacitor 33 which is utilized to tune the coil 32 sothat a maximum signal is coupled through the coil 32 to a winding 34.The winding 34 form-s part of an antenna 35, together with a loadingcoil 36. The adjustable capacitor 33 may have a range similar to that ofthe adjustable capacitor 27.

The two capacitors 27 and 33, Vone in the radio frequency oscillatoritl, and the other across the coil 32, are adjusted to provide themaximum output signal utilizing a DnC. meter di) which is connected tothe coil 32. The june-tion between the coil 32 and the meter it? iscoupled to ground by a capacitor 4l which may have arvalue of .005microfarad. The capacitor il serves to shunt the radio frequency signalprovided toward the meter it? to ground so that the meter dil iseffectively RF decoupled from the coil 32.

The meter dii connects the coil 32 to the audio frequency oscillator 12,briefly mentioned above. The audio oscillator 12 includes a transistorSi? as its active element, which may be of the type designated R456manufactured by the Texasv Instrument Company, and also an 3auto-transformer l which is connected to the meter dit. The oscillatorl" develops, illustratively, a 1,000 cycle tone utilizing theauto-transformer 5i as part of the feedback path together with a windingS2 between the collector and emitter' electrodes of the grown diffusedtransistor 5d. The emitter electrode of the transistor 59 is connectedto the winding S2 by Ian emitter resistor 53 which may have a value of27 ohms. The other terminal of the winding 52 is connected to ground.The autotransformer 5l is resonated at the 1,800 cycle frequency due toa capacitor 55 which is coupled from one end of the auto-transformer atits terminal 4 to a terminal 2 adiacent to its other end. The capacitor5S resonates the auto-transformer S1 to develop a substantiallysinusoidal audio signal to the meter at?.

The following are illustrative values for the auto-transformer windingsand the winding 52:

Terminals 3 to 4-.8 to 1.2 henries, 225 ohms DC. max.; 'Terminals 3 to 1100 ohms, DC. Max.; Terminals 3 to 2-37 ohms DC. max.; and Winding 52--5ohms DE. max.

Illustrative turns ratios are as follows:

Terminals 3 to 1 and Terminals 3 to 4 ll- Winding 52 l The baseelectrode of the transistor 50 is connected to ground by a capacitor 5Swhich may have a value of 0.1 microfarad and the collector electrode isconnected to terminal l of the auto-transformer 51. The capacitor 5Sserves to provide for a substantially constant or uniform amplitude withvariations of transistor characteristics. ferent transistors. The baseelectrode is also connected to ground by a rheostat 59 which is utilizedto adjust the amplitude of the signal delivered by the audio oscillatorl2. The rheostat 59 may have a maximum resistance of 1.5 kilohms. Thebase electrode is biased over a path from the switch through a resistor60 which may have a value of 39 kilohms. The biasing potential at thebase electrode may be |0-9 volt. The radio frequency signal at theoscillator 16 is shunted about the source la through a by-pass capacitor64 which may have a value of 0.005 microfarad.

rThe oscillator 12 delivers a considerable amount of power,illustratively, 50 milliwatts to function as a combined power amplifierand oscillator so that a 100 percent modulation may be achieved of theradio frequency signal delivered from the RF ampliiier l1. The powerutilized by the transistor 30 may also be 100 milliwatts. The poweramplification is achieved, in part, by resonating the auto-transformer51. The capacitor 5S, accordingly, serves both to provide the sinusoidalwave shape and to enhance the power provided to the meter 40.

The sinusoidal audio signal is provided from across the terminals 2 and3 of the auto-transformer 5l to the DC. meter 40. As indicated above,the meter 49 is utilized when the capacitors 27 and 33 are adjusted. The inductance of the meter liti serves as part of the RF signaldecoupling circuitry together with the capacitor 41, and the resistanceof the meter 49 serves as part of the serial arrangement together withthe coil 32 to provide for the modulation. The resistance of the meter46 forms the serial arrangement with the coil 3?. so that the signalacross the coil is modulated by the audio frequency. More particularly,the biasing circuit for the Further, the amplitude remains constant fordif-V collector of the transistor' 3i) is from the s'ource 14 throughthe switch l5, the portion of the auto-transformer 5l between itsterminals 2 and 3, the meter 40 and the lower portion of the coil 32..The bias to the collector electrode is varied by the audio frequencysignal generated between the terminls 2 and 3 of the autotransformer 51.The ampliiier l, coil 32 and meter 40, accordingly, function together asa modulated radio frequency amplifier. The transformer 5l and amplifierl2 function together as a modulator.

Although this invention has been disclosed and illustrated withrefe-rence to particular applications, the principles involved aresusceptible of numerous other applications which will be apparent topersons skilled in the art. The invention is, therefore, to be limitedonly as indicated by the scope of the appended claims.

l claim:

l. A radio transmitter having a crystal RF oscillator for generating aconstant frequency RF signal, a RF arnplier coupled to said oscillatorand including a first tra `istor having three electrodes, a biasing pathconnected to each of said three electrodes, and a RF output coilconnected to one of said three electrodes; said biasing circuit for saidone electrode including a portion of said output coil; an ntenna cou ledto said output coil, an audio frequency oscillator for providing anaudio frequency modulating signal and including an auto-transformercoupled to said output coil for introducing the modulating signal tosaid output coil, a second transistor having three electrodes, a biasingcircuit connected to each of said three electrodes of said secondtransistor, one of said electrodes of said second transistor beingconnected to said auto-transformer so that at least a portion of saidauto-transformer is included in the biasing circuit connected to saidone electrode of said second transistor, RF decoupling means connectedbetween said output coil and said auto-transformer for preventing theintroduction of the RF signal to said auto-transformer, a source ofbiasing potential connected to said auto-transformer whereby saidbiasing circuit for said one electrode of said first transistor includessaid source, a portion of said auto-transformer, said RF decouplingmeans, said portion of said output coil, said decoupling means includinga DC. meter having both inductance and resistance and said audiofrequency oscillator also including a capacitor connected across aportion of the auto-transformer for resonating said auto-transformer atthe audio frequency.

2. A radio transmitter having a RF oscillator for generating an RFsignal, aRF amplifier coupled to said RF oscillator for amplifying saidRF signals, a tuned circuit coupled to said amplifier which is tuned tothe frequency of said RF oscillator, and an audio frequency oscillatorfor providing an audio frequency modulating signal, coupling meansconnected between said audio frequency oscillator and said tuned circuitand including a resistive element for introducing the audio frequency inseries with the signal across the tuned circuit whereby said RF signalat said tuned circuit is modulated by the audio frequency signal, and ameter constituting the element in the coupling means and the meter beingprovided with an inductive reactance to inhiiirtte transfer of energyfrom the tuningcircuit to the audio oscillator.

3. Auiad'io L"t'ra'isi'nwi ter having a crystal RF oscillator forgenerating a constant frequency RF signal, a RF ampliiier coupled tosaid oscillator and including a first transistor having threeelectrodes, a biasing path connected to each of said three electrodes,and a RF output coil connected to one of said three electrodes; saidbiasing circuit for said one electrode including a portion of saidoutput coil; an antenna coupled to said output coil, an audio frequencyoscillator for providing an audio frequency modulating signal andincluding an auto-transformer coupled to said output coil forintroducing the modulating signal to said output coil; RF decoupling r.'o means connected between said output coil and said autotransformer forpreventing the introduction of the RF signal t0 said auto-transformer, asource of biasing p0- tential connected to said auto-transformer wherebysaid biasing circuit for said one electrode of said first transistorincludes said source, a portion of said auto-transformer, said RFdecoupling means, said portion of said output coil, and the decouplingmeans including a meter having resistive and inductive components toinhibit the introduction of the RF signal to the auto-transformer.

References Cited in the file of this patent UNITED STATES PATENTS TermanApr. 15, Coxey May 25, Koros July 7, Kircher Sept. 23, Lin Oct. 7,Carroll et al. Aug. 18,

Bryan Oct. 4,

1. A RADIO TRANSMITTER HAVING A CRYSTAL RF OSCILLATOR FOR GENERATING A CONSTANT FREQUENCY RF SIGNAL, A RF AMPLIFIER COUPLED TO SAID OSCILLATOR AND INCLUDING A FIRST TRANSISTOR HAVING THREE ELECTRODES, A BIASING PATH CONNECTED TO EACH OF SAID THREE ELECTRODES, AND A RF OUTPUT COIL CONNECTED TO ONE OF SAID THREE ELECTRODES; SAID BIASING CIRCUIT FOR SAID ONE ELECTRODE INCLUDING A PORTION OF SAID OUTPUT COIL; AN ANTENNA COUPLED TO SAID OUTPUT COIL, AN AUDIO FREQUENCY OSCILLATOR FOR PROVIDING AN AUDIO FREQUENCY MODULATING SIGNAL AND INCLUDING AN AUTO-TRANSFORMER COUPLED TO SAID OUTPUT COIL FOR INTRODUCING THE MODULATING SIGNAL TO SAID OUTPUT COIL, A SECOND TRANSISTOR HAVING THREE ELECTRODES, A BIASING CIRCUIT CONNECTED TO EACH OF SAID THREE ELECTRODES OF SAID SECOND TRANSISTOR, ONE OF SAID ELECTRODES OF SAID SECOND TRANSISTOR BEING CONNECTED TO SAID AUTO-TRANSFORMER SO THAT AT LEAST A PORTION OF SAID AUTO-TRANSFORMER IS INCLUDED IN THE BIASING CIRCUIT CONNECTED TO SAID ONE ELECTRODE OF SAID SECOND TRANSISTOR, RF DECOUPLING MEANS CONNECTED BETWEEN SAID OUTPUT COIL AND SAID AUTO-TRANSFORMER FOR PREVENTING THE INTRODUCTION OF THE RF SIGNAL TO SAID AUTO-TRANSFORMER, A SOURCE OF BIASING POTENTIAL CONNECTED TO SAID AUTO-TRANSFORMER WHEREBY SAID BIASING CIRCUIT FOR SAID ONE ELECTRODE OF SAID FIRST TRANSISTOR INCLUDES SAID SOURCE, A PORTION OF SAID AUTO-TRANSFORMER, SAID RF DECOUPLING MEANS, SAID PORTION OF SAID OUTPUT COIL, SAID DECOUPLING MEANS INCLUDING A D.C. METER HAVING BOTH INDUCTANCE AND RESISTANCE AND SAID AUDIO FREQUENCY OSCILLATOR ALSO INCLUDING A CAPACITOR CONNECTED ACROSS A PORTION OF THE AUTO-TRANSFORMER FOR RESONATING SAID AUTO-TRANSFORMER AT THE AUDIO FREQUENCY. 